Introduction: Adipose stem cells (ASCs) secrete many trophic factors that can stimulate tissue repair, including\r\nangiogenic factors, but little is known about how ASCs and their secreted factors influence cartilage regeneration.\r\nTherefore, the aim of this study was to determine the effects ASC-secreted factors have in repairing chondral\r\ndefects.\r\nMethods: ASCs isolated from male Sprague Dawley rats were cultured in monolayer or alginate microbeads\r\nsupplemented with growth (GM) or chondrogenic medium (CM). Subsequent co-culture, conditioned media, and\r\nin vivo cartilage defect studies were performed.\r\nResults: ASC monolayers and microbeads cultured in CM had decreased FGF-2 gene expression and VEGF-A\r\nsecretion compared to ASCs cultured in GM. Chondrocytes co-cultured with GM-cultured ASCs for 7 days had\r\ndecreased mRNAs for col2, comp, and runx2. Chondrocytes treated for 12 or 24 hours with conditioned medium\r\nfrom GM-cultured ASCs had reduced sox9, acan, and col2 mRNAs; reduced proliferation and proteoglycan synthesis;\r\nand increased apoptosis. ASC-conditioned medium also increased endothelial cell tube lengthening whereas\r\nconditioned medium from CM-cultured ASCs had no effect. Treating ASCs with CM reduced or abolished these\r\ndeleterious effects while adding a neutralizing antibody for VEGF-A eliminated ASC-conditioned medium induced\r\nchondrocyte apoptosis and restored proteoglycan synthesis. FGF-2 also mitigated the deleterious effects VEGF-A\r\nhad on chondrocyte apoptosis and phenotype. When GM-grown ASC pellets were implanted in 1 mm non-critical\r\nhyaline cartilage defects in vivo, cartilage regeneration was inhibited as evaluated by radiographic and equilibrium\r\npartitioning of an ionic contrast agent via microCT imaging. Histology revealed that defects with GM-cultured ASCs\r\nhad no tissue ingrowth from the edges of the defect whereas empty defects and defects with CM-grown ASCs\r\nhad similar amounts of neocartilage formation.\r\nConclusions: ASCs must be treated to reduce the secretion of VEGF-A and other factors that inhibit cartilage\r\nregeneration, which can significantly influence how ASCs are used for repairing hyaline cartilage.
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